In fabrication of semiconductor devices, semiconductor wafers are repeatedly subjected to various processes, such as film formation, etching, heat treatment, modification, and the like. As a film formation process in which a thin film is formed on a surface of a semiconductor wafer, there is chemical vapor deposition (CVD) in which the semiconductor wafer is placed within a process chamber of a processing apparatus, and a gas including a source gas is introduced to the process chamber to generate a reaction product, so that the reaction product can be deposited on the surface of the semiconductor wafer.
Recently, the film formation has been also carried out through atomic layer deposition in which a source gas and a reaction gas are alternately supplied to a process chamber to form thin films each having an atomic level or molecular level of thickness layer by layer. Since providing good quality of films and enabling an adjustment of the film thickness with high accuracy, ALD has attracted attention as a method for fabricating a semiconductor device to which miniaturization is underway.
Here, one example of formation of a TiN film by an ALD method will be described. In this example, TiN thin films are deposited by repeating a series of processes (1) to (4), so that a TiN film having a desired thickness is obtained.
(1) A source gas, for example, TiCl4 gas, is supplied to a process chamber, so that TiCl4 is attached to a surface of a wafer.
(2) The remaining source gas is removed from the process chamber by purging the process chamber with N2 gas.
(3) A TiN thin film having an atomic level or molecular level of thickness is formed by supplying a reaction gas, for example, NH3 gas, to the process chamber for reaction with TiCl4 attached to the surface of the wafer.
(4) The remaining gas is removed from the process chamber by purging the process chamber with N2 gas.
In the film formation by the ALD method, as described above in formation of the TiN film, supplying plural gases including the source gas and stopping the gas supply must be intermittently performed for a short period of time. In an ALD apparatus which is a film formation apparatus using an ALD method, supply of gas and stop thereof are performed by a controller, wherein the controller sends signals based on a gas supply recipe to an electronic valve which is installed in a gas supply channel through which the gas leads to the process chamber, so as to open or close the electronic valve.
In the film formation apparatus using the ALD method, a time for which one gas is supplied to the process chamber is shorter than that in a film formation apparatus using a CVD method. As a result, in order to form a film having high in-plane uniformity in the film formation using the ALD method, it is necessary to supply a gas under conditions which can increase uniformity of the gas concentration near the wafer within a short period of time after the start of supplying the gas to the process chamber.
Technologies for forming a film having high in-plane uniformity in the film formation using the ALD method are disclosed in the related art.
For example, a gas supply apparatus disclosed in a first related art includes a main body that defines a gas flow passage space having a substantially conical shape to allow a gas to flow therethrough from a small diameter end to a large diameter end, a gas inflow port provided to the small diameter end of the flow passage space to introduce the gas into the flow passage space, and partition members partitioning the flow passage space in a concentric circle shape such that a radially outer side is greater in dimensional diverging rate.
In addition, a film formation apparatus disclosed in a second related art includes a central gas ejection portion disposed above a central region of a substrate, and a surrounding gas supply unit disposed to surround the central gas ejection portion.
Further, an atomic layer formation apparatus disclosed in a third related art includes a plurality of gas supply conduits for supplying a gas including a raw material for forming a thin film on a substrate into a film formation chamber, a plurality of valves respectively provided to the plurality of gas supply conduits, a plurality of film formation chamber monitors monitoring conditions of the film formation chamber, and a controller individually controlling opening degrees or opening times of the plurality of valves based on monitoring results of the plurality of film formation chamber monitors.
According to the first and second conventional technologies, the same kind of gas can be ejected from a plurality of different locations towards the surface of a wafer, thereby enabling the gas to widely spread over the surface of the wafer.
However, it is difficult to say that a film having high in-plane uniformity can be sufficiently formed by the first and second conventional technologies in the film formation using the ALD method. The following reasons are provided. In the first and second conventional technologies, the gas having passed through one gas supply conduit is supplied into a plurality of branches, which in turn are ejected from a plurality of different locations. In these technologies, durations for which the plurality of branch gases are ejected are controlled only by one valve provided to one gas supply conduit.
As described above, in order to form a film having high in-plane uniformity in the film formation using an ALD method, it is necessary to supply a gas under conditions which can increase uniformity of the gas concentration near the wafer within a short period of time after the start of supplying the gas to the process chamber. In the first and second conventional technologies, however, since the durations of ejecting the plurality of branch gases are controlled only by one valve provided to one gas supply conduit, it is difficult to accurately control the gas distribution near the wafer such that those conditions can be met.
Moreover, although not clearly disclosed in the third conventional technology, it is thought from an object of the technology described in the third conventional technology that the same kind of gases are supplied to the film formation chamber substantially at the same time through a plurality of gas supply conduits in the atomic layer formation apparatus. Accordingly, it is thought that a source gas, an oxidation gas, and a purge gas are supplied while being switched to the same plural gas supply conduits and, thus the gases are supplied while being switched to the film formation chamber in this atomic layer formation apparatus. In this method, since complete switching between the gases in the plurality of gas supply conduits takes time, switching between the gases being supplied into the film formation chamber also takes time, thereby causing a problem of time consumption in film formation.